Nonbonded potential parameters for intermolecular interactions in amino acids and petides are to be obtained, primarily from crystal structure data already available in the literature. The criterion of accuracy is the achievement of threshold level fits to the observed crystal structures. The method is extended to include weak bonding, especially the hydrogen bond. The crystal structure data is to be supplemented by quantum mechanical calculations of the molecular electric field and the energy of molecular dimerization. The results of these calculations are to be used to assist in the assignment of net atomic charges, and in modelling the hydrogen bond interaction. The resulting potential energy functions are designed to be suitable for use in the calculation of protein conformation and the energy and geometry of protein-substrate interaction.